As mentioned earlier, only once before has an authentic Buddha’s relic been brought over to Japan. It was in July 1900 when the king of Siam donated it to the Buddhist society in Japan.
There was a second time the Buddha’s relic was brought over to Japan.
On April 7, 1986, the president of Sri Lanka (formerly known as Ceylon) officially donated a Buddha’s relic. As noted in the official document, this relic is equivalent to the Buddha’s relic donated previously by the king of Siam. It had been enshrined at Bodhgaya, the place of Shakyamuni Buddha’s attainment of Enlightenment. (For details of the documents, see "Shugorei-no Keifu (Genealogy of Guardian Spirits" by Seiyu Kiriyama published by Hirakawa Shuppan, Inc.)

Agon Shu is strangely linked by fate to Buddha’s relics. Since over ten years ago, Buddha’s relics were donated to Agon Shu one right after another. In 1974, the five pieces of Buddha’s relic that were enshrined at the Daihonzan Temple in the Tokai Region since the early Meiji Era (1868 – 1912) were donated by some follower. (The ancestor of two generations ago enshrined these relics, but the resident Buddhist priest was negligent in his training. As a result, the relics were taken back and donated to Agon Shu. Some of the relics are enshrined at Kurinto, the top of the (former) Tokai Main Center.

Since then, Buddha’s relics were donated to Agon Shu one right after another almost every year. Among them, the Buddha’s relic donated in 1979 by the Sudas, the ruling family of Aizu, had an official document stating that Kobodaishi Kukai brought it over from China. Among them contained a piece of golden relic. While I have seen and worshipped nearly a hundred pieces of Buddha’s relics, I have never seen a relic like this one before. This one was quite different from the other relics.
Following this, Agon Shu received several pieces of Buddha’s relics from the Dalai Lama in March 1983. The official document by the government of the Dalai Lama states that they are the authentic Buddha’s bones.
Next, we received the Buddha’s bones from Sri Lanka on April 7, 1986.

(snip)

As mentioned earlier, I have worshipped nearly a hundred pieces of the Buddha’s relics, but the Buddha’s relics received from the Dalai Lama and the president of Sri Lanka are unprecedented. They are quite different from the others. They are unmistakably Buddha’s relics. Among the Buddha’s relics brought over by Kobodaishi Kukai, the golden piece is really different. It appears to be either a stone or bead, but at the same time it is neither a stone nor a bead and is quite magical. The reason I do not officially name this golden piece of relic an authentic Buddha’s relic is partly because it is difficult to determine its history and affirm its heirloom from a long time ago. However, I truly believe that this golden piece of relic is the very Buddha’s relic that Kobodaishi Kukai brought over to Japan.